Tl(III) initiated polymerization of methyl methacrylate in micellar phase

The polymerization kinetics of methyl methacrylate (MMA) was studied, using Tl(III)‐cyclohexanone (CH) redox system as initiator, in the presence of emulsifier [i.e., sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and thallium triacetate (TX‐100)] over a temperature range of 25–45°C. The effect of various concentrations of MMA, Tl(III), cyclohexanone, H⁺, and varying ionic strengths on the rate of polymerization, rate of Tl(III) consumption (?R_Tl), and the percentage of monomer conversion were examined in the presence of 0.015M SDS. The kinetic results of polymerization in the absence and presence of 0.015M SDS were compared in terms of overall activation energy (E_a) for the process. The viscosity‐average molecular weight (M_V) of the polymers, obtained in the presence of varying concentrations of anionic surfactant (SDS), was also determined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2480–2485, 2004     

Analysis of microstress in neutron irradiated polyester fibre by X-ray diffraction technique

Microstresses developed in the crystallites of polymeric material due to irradiation of high-energy particle causes peak broadening and shifting of X-ray diffraction lines to lower angle. Neutron irradiation significantly changes the material properties by displacement of lattice atoms and the generation of helium and hydrogen by nuclear transmutation. Another important aspect of neutron irradiation is that the fast neutron can produce dense ionization at deep levels in the materials. The polyethylene terephthalate (PET) fibre of raw denier value, 78.2, were irradiated by fast neutron of energy, 4.44 MeV, at different fluences ranging from 1×10⁹ n/cm² to 1 × 10¹² n/cm². In the present work, the radiation heating microstresses developed in PET micro-crystallites was investigated applying X’Pert-MPD Philips Analytical X-ray diffractometer and the effects of microstresses in tensile strength of fibre measured by Instron have also been reported. The shift of 0.45 cm⁻¹ in the Raman peak position of 1614.65 cm{−1} to a higher value confirmed the development of microstresses due to neutron irradiation using micro-Raman technique. The defects due to irradiation were observed by SEM micrographs of single fibre for virgin and all irradiated samples.     

Macroporous SiOC Ceramics with Dense Struts by Positive Sponge Replication Technique

Highly porous SiOC ceramics (≥90% open porosity) containing dense struts have been prepared following positive sponge replication technique using silsesquioxane based preceramic polymer. The morphological features including cell size, cell window size, and strut size of the macroporous SiOC ceramics have been analyzed using electron microscopy. Subtle variation in the crosslinking condition of the preceramic polymer infiltrated polyurethane template enables the formation of hollow as well as dense struts, which has a profound influence on compressive strength of the macroporous bodies. Synchrotron radiation micro computed tomography is used to construct the three dimensional images of the macroporous ceramics that indicate isotropy of the pores and excellent interconnectivity.

     

Synthesis,structure and thermoelectric properties of $$\mathrm{La}_{1-x}\mathrm{Na}_{x}\mathrm{CoO}_{3 }$$ perovskite oxides

Monovalent ion doped lanthanum cobaltate \(\hbox {La}_{1-x}\hbox {Na}_{x}\hbox {CoO}_{3 }\) (\(0 \le x \le 0.25\)) compositions were synthesized by the nitrate–citrate gel combustion method. All the heat treatments were limited to below 1123 K, in order to retain the Na stoichiometry. Structural parameters for all the compounds were confirmed by the Rietveld refinement method using powder X-ray diffraction (XRD) data and exhibit the rhombhohedral crystal structure with space group R-3c (No. 167). The scanning electron microscopy study reveals that the particles are spherical in shape and sizes, in the range of 0.2–0.5 \(\upmu \)m. High temperature electrical resistivity, Seebeck coefficient and thermal conductivity measurements were performed on the high density hot pressed pellets in the temperature range of 300–800 K, which exhibit p-type conductivity of pristine and doped compositions. The X-ray photoelectron spectroscopy (XPS) studies confirm the monotonous increase in \(\hbox {Co}^{4+}\) with doping concentration up to \(x = 0.15\), which is correlated with the electrical resistivity and Seebeck coefficient values of the samples. The highest power factor of \(10~\upmu \hbox {W~mK}^{-2 }\) is achieved for 10 at% Na content at 600 K. Thermoelectric figure of merit is estimated to be \({\sim }1 \times 10^{-2}\) at 780 K for 15 at% Na-doped samples.     

Drop Calorimetric Measurements on Binary Bi–In System

Measurements of integral enthalpies of mixing of Bi–In system have been taken at 767, 813 and 855 K by a drop calorimeter over the entire composition range. Bismuth was used as the base metal, and indium was dropped by motorized dropping device. Calibration of the calorimeter was done by dropping four pieces of α-Al₂O₃ at the drop temperatures. The measured enthalpies of mixing are plotted against indium composition and found exothermic in nature for all the compositions. The minimum enthalpies were observed in the range of compositions x_In?~?0.40–0.50. A slight temperature dependency of enthalpy was observed for each composition. The experimental data were used to determine the binary interaction parameters using Redlich–Kister polynomial at 767, 813 and 855 K.     

Sintering and microstructural study of mullite prepared from kaolinite and reactive alumina: Effect of MgO and TiO2

Mullite ceramic was prepared using kaolinite and synthesized alumina (combustion route) by solid-state interaction process. The influence of TiO₂ and MgO additives in phase formation, microstructural evolution, densification, and mechanical strengthening was evaluated in this work. TiO₂ and MgO were used as sintering additives. According to the stoichiometric composition of mullite (3Al₂O₃·2SiO₂), the raw materials, ie kaolinite, synthesized alumina, and different wt% of additives were wet mixed, dried, and uniaxially pressed followed by sintering at different temperature. 1600°C sintered samples from each batch exhibit enhanced properties. The 1 wt% TiO₂ addition shows bulk density up to 2.96 g/cm³ with a maximum strength of 156.3 MPa. The addition of MgO up to 1 wt% favored the growth of mullite by obtaining a density and strength matching with the batch containing 1 wt% TiO₂. These additives have shown a positive effect on mullite phase formation by reducing the temperature for complete mullitization by 100°C. Both additives promote sintering by liquid phase formation. However, the grain growth, compact microstructure, and larger elongated mullite crystals in MgO containing batch enhance its hardness properties.     

Dielectric and impedance properties of LiCa2Nb5O15 ceramics

Polycrystalline sample of LiCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500 °C) and frequency (10²–10⁶ Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity.     

Recovery of copper values from bio-heap leaching of low grade Malanjkhand chalcopyrite ore

M/S Hindustan Copper Limited (HCL), India generates large amounts of lean sulfide ores of copper. The current production of lean copper ores in India is 0.55 million tons with ∼0.3% average copper content. Heap-bioleaching of the lean copper ores in 15 and 30 ton scales was undertaken at IMMT, Bhubaneswar. The leaching study showed 0.09% dissolution of copper from the ore body per day. The leach liquor was processed through solvent extraction and electrowinning. Extraction of copper from the actual leach liquor was carried out with 1.5% LIX 622N in kerosene with zero co-extraction of iron. The copper-free raffinate was fed back to the leaching unit. Stripping of copper from the loaded organic was carried out with 180 kg/m³ H₂SO₄. The copper pregnant electrolyte was passed through a carbon column to make it free from entrained organic and was fed to the electrowinning unit. The increase in current efficiency was due to the increase in the concentration of electrolyte. The energy consumption was 1.7 kWh/kg at a flow rate of 4.5 L/h. Smooth and bright sheets of copper of 99.99% purity were obtained.     

Design of multi-frequency microstrip antennas using multiple rings

An electromagnetically coupled feed arrangement is proposed for simultaneously exciting multiple concentric ring antennas for multi-frequency operation. This has a multi-layer dielectric configuration in which a transmission line is embedded below the layer containing radiating rings. Energy coupled to these rings from the line beneath is optimised by suitably adjusting the location and dimensions of stubs on the line. It has been shown that the resonant frequencies of these rings do not change as several of these singlefrequency antennas are combined to form a multi-resonant antenna. Furthermore, all radiators are forced to operate at their primary mode and some harmonics of the lower resonant frequency rings appearing within the frequency range are suppressed when combined. The experimental prototype antenna has three resonant frequencies at which it has good radiation characteristics.     

Equilibria involving the reciprocal spinel solid solution (Mg x Fe1−x ) (Al y Cr1−y )2O4: modeling and experiment

Developed in this article is a model for calculating cation distribution and activities in the reciprocal spinel solid solution (Mg _X Fe_1−X )(Al _Y Cr_1−Y )₂O₄ based on octahedral site preference energies of cations independent of composition and temperature, random distribution of ions on tetrahedral and octahedral sites, entropy of randomization of Jahn-Teller distortions associated with Fe²⁺ ions on the tetrahedral site, and the standard Gibbs energies of formation of the four pure spinel compounds. Enthalpy of mixing of this reciprocal solid solution caused by the large difference of ionic radii of Al³⁺ and Cr³⁺ present on the octahedral site was modeled based on experimental data on the binary systems. The tie-line compositions corresponding to the equilibria between the spinel solid solution and the sesquioxide solid solution (Al _Z Cr_1−Z )₂O₃ with corundum structure were computed. Values for activities in the corundum solid solution were taken from the literature. The oxygen potential corresponding to the three-phase equilibrium involving metallic iron, the spinel solid solution, and corundum solid solution was computed as a function of composition of the spinel solid solution. The computed results were verified by measurements on nine compositions inside the square representing the reciprocal system. The compositions of coexisting solid solutions were determined by electron-probe microanalysis (EPMA) and lattice parameter measurement using X-ray diffraction (XRD). The activities of FeAl₂O₄ and FeCr₂O₄ and oxygen potentials for three-phase equilibria were measured using two independent solid-state cells incorporating a bielectrolyte chain. Both cells gave consistent results within experimental error. The experimental results are in excellent agreement with the computed results, thus validating the model for the reciprocal spinel solid solution.